How was James Fields convicted, then? The feds have countless possible charges to bring in cases like this, from conspiracy/RICO charges to ‘civil rights intimidation’ charges. Thus far, they are choosing not to act against violent leftists. This is a policy choice, not a matter of law.
James Fields’ crimes involved interstate travel - he drove to Charlottesville from Ohio with the specific intent to commit crimes, thus invoking Federal jurisdiction. Interstate commerce.